9307068 Gastony Difficulties in identifying natural evolutionary lineages in homosporous ferns and in circumscribing these lineages as genera and families are often attributed to the effects of convergent and parallel evolution on the morphological characters traditionally used in fern taxonomy. The cheilanthoid ferns, largely adapted to semi desert conditions or to other seasonally dry habitats, are the foremost examples of this. Molecular data from the chloroplast genome are unaffected by habitat related selective forces acting on morphology and are beginning to yield fundamental insights into fern evolution and phylogeny. However, recent studies on flowering plants have found some instances in which hybridization, introgression, or lineage sorting may lead to significant error in phylogenetic reconstructions based solely on the cytoplasmically inherited chloroplast genome. This raises concern for ferns because the high incidence of allopolyploid hybrids and high basic chromosome numbers in ferns suggest that modern ferns may be paleopolyploids in whose ancestry reticulate evolution has been important. Dr. Gastony's project will serve as a model study for homosporous ferns by using cladistically analyzed molecular data from chloroplast DNA (nucleotide sequences of the rbc L gene) to provide fundamental new insights into cheilanthoid fern relationships and phylogeny. Importantly also, the project will use molecular data f rom the nuclear genome (nucleotide sequences of ribosomal DNA) to compare with chloroplast DNA results and with traditional morphological characters. %%% The combined morphological and molecular data will form the basis of a revised classification of cheilanthoid ferns and of a robust reconstruction of their phylogenetic relationships, on a worldwide basis.
